1. Field of the Invention
The present invention relates to a bogie truck axlebox suspension system for a railroad vehicle and particularly relates to an axlebox suspension system adapted to a truck which needs a steering function.
2. Prior Art
A conventional railroad vehicle is designed so that each pair of left and right wheels are fixed to a corresponding axle so as to rotate at equal rotational speeds. Further, in the conventional railroad vehicle, there are provided slopes called "wheel treads" at contact portions between the wheels and rails so that, when the wheels run on curved portions of the rails, a corresponding wheelset is displaced to the outside of the curve by the action of centrifugal force, or the like, to thereby cause a difference between the turning radii of inner and outer wheels to suppress the sliding of the inner and outer wheels on the rails to be in a fine range. Further, in the case of an acute curve in the railroad, enlargement of the distance between railroad tracks, which is called "slack", is provided so that the difference between the turning radii of the inner and outer wheels increases more greatly. Thus, as described above, the wheels per se have self-steering property. A conventional bogie truck is, however, characterized in that an axlebox suspension system with longitudinal stiffness is provided between a truck frame and an axlebox in order to prevent snaking from occurring at the time of high-speed running on a straight line portion. Further, in view of mechanism, the opposite ends of the axle are elastically fastened to the truck frame. As a result, in the case where the respective axles are to be directed to the center of the curve when the axles pass the curve in the railroad, force exceeding the elastic force of suspension is required to be transmitted. Therefore, a mechanism for connecting the axles and the truck frame through links is used, for example, as described in JP-A-5-77730.
Those systems become, however, so complex in structure as to bring increase in weight, production cost and maintenance cost in comparison with ordinary trucks. Accordingly, those systems are only used for a limited purpose of special express trains such as JR Hokkaido 283 railroad motor cars, or the like, requiring a high-speed operation.
An object of the present invention is therefore to provide an axlebox suspension system in which the aforementioned motion of the axles can be performed by paying attention to the characteristic of axles in that rotational displacement in a horizontal plane around the respective centers of gravity of the axles is made, while keeping the distance between the centers of the axles constant with respect to a truck frame in the case where the axles are turned toward the center of a curve in the railroad.